Reports emerge that steroids may have been found at Pistorius’ home the night he shot and killed his girlfriend.

Police sources told the South AfricaTimes that drugs and syringes were found in a drawer in Pistorius’ bedroom. Pistorius admitted to fatally shooting girlfriend Reeva Steenkamp on Valentine’s Day but claimed he mistook her for an intruder. He was immediately taken for blood and urine tests after his arrest on Feb. 14. The paper reports that the Olympian’s lawyers may be considering a “roid rage” defense, arguing that Pistorius was under the influence of steroids, which can cause paranoia, jealousy, aggression and irritability, when he shot Steenkamp. Although Steven Tuson, a professor of criminal law at Johannesburg’s Wits University told Reuters that a “roid rage” defense is unlikely to succeed, there is some evidence that synthetic versions of naturally-occurring steroids could trigger unusually aggressive behavior.

Human studies exploring this connection, however, are limited. In a 2008 study, Kevin Beaver, an associate professor at The Florida State University College of Criminology and Criminal Justice and his colleagues analyzed data from the National Longitudinal Study of Adolescent Health involving 20,000 participants and found that steroid users were approximately twice as likely to engage in violent behavior, such as getting into physical fights.

Another study from researchers at Northeastern University revealed that hamsters using steroids behaved more aggressively, and had significantly lower levels of the “feel good” receptor, serotonin, in areas of the brain related to aggression and violence.

Still, the extent to which steroid abuse contributes to violence remains unknown. There are not enough human studies to determine how much of an influence steroids play in triggering aggressive responses vs. other circumstances or factors that steroid-takers might share in common, and who might be most vulnerable to the effects of the drugs. “I think part of the reason for a lot of debate coming out is that we simply don’t know the [biological] mechanisms. If we did, there would be a lot more consensus,” says Beaver.

But there are intriguing connections between changes in hormone and brain chemical levels and an increased tendency toward violent behaviors. In a recent study, Neil MacLusky, a professor at the University of Guelph in Ontario found that high levels of testosterone in mice, for example, suppresses the brain-derived neurotrophic factor (BDNF) that is involved in depression and inappropriate reactions to stimuli in humans. The results suggest that increased testosterone, which belongs to a family of steroid hormones called androgens, can alter mood, in some cases perhaps even promoting more aggressive tendencies. “These are hypothesizes of course and absolutely not proven for people,”says MacLusky. “Just as people vary a great deal in the extent to which they are predisposed to depression, this may be why people vary a great deal in their response to androgens.”

MacLusky argues that reactions to androgens may differ from person to person. “It may be in some cases, that treatment with high-dose androgens, like the things athletes have been doing, may increase aggression in some cases, but it is clearly not true for everybody,” he says. “There is some indication from both animal and human studies that it may be the particular type of androgen used. Or there may be different effects depending on what particular treatment a person is using, but it may also just be differences between people. Some people are more susceptible than others. It’s a complicated situation.”

Even if Pistorius’ legal team considers a “roid rage” defense, the gap in human studies means it won’t be easy to make their case.